The present invention is generally directed to toner processes, and more specifically, to aggregation and coalescence processes for the preparation of toner compositions. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 1 to about 25 and preferably from 1 to about 10 microns, and narrow GSD characteristics can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally a charge control agent or additive in an aqueous mixture containing an ionic surfactant, and shearing this mixture with a latex mixture, comprised of suspended resin particles of from about 0.05 micron to about 2 microns in volume diameter, in an aqueous solution containing a counterionic surfactant with opposite charge to the ionic surfactant of the pigment dispersion and nonionic surfactant, thereby causing a flocculation of resin particles, pigment particles and optional charge control particles, followed by stirring of the flocculent mixture, which is believed to form statically bound aggregates of from about 0.5 micron to about 5 microns, comprised of resin, pigment and optionally charge control particles, and thereafter heating to generate toners with an average particle volume diameter of from about 1 to about 25 microns. It is believed that during the heating stage, the aggregate particles fuse together to form toners. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant such as benzalkonium bromide (SANIZOL B-50.TM.), utilizing a high shearing device such as a Brinkman Polytron, or microfluidizer or sonicator; thereafter shearing this mixture with a latex of suspended resin particles, such as PLIOTONE.TM., comprised of styrene butadiene and of particle size ranging from 0.01 to about 0.5 micron as measured by the Brookhaven nanosizer, in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.TM. or NEOGEN SC.TM.), and nonionic surfactant such as alkyl phenoxy poly(ethylenoxy)ethanol (for example IGEPAL 897.TM. or ANTAROX 897.TM.), thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which on further stirring results in formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II); and thereafter, heating to provide for particle fusion or coalescence of the polymer and pigment particles; followed by washing with, for example, hot water to remove surfactant, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to 12 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is formed by the neutralization of the pigment mixture containing the pigment and cationic surfactant absorbed on the pigment surface, with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. The high shearing stage disperses the big initially formed flocculants, and speeds up formation of stabilized aggregates negatively charged and comprised of the pigment and resin particles of about 0.5 to about 5 microns in volume diameter. Thereafter, heating is applied to fuse the aggregated particles or coalesce the particles to toner composites. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by homogenization; and form statically bound aggregate particles by stirring of the homogeneous mixture and toner formation after heating.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with an average volume particle of less than 11 microns and preferably less than about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.2 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized such as pictorial color applications, small particle size colored toners of from about 3 to about 9 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes such as from about 1 to 7 microns and with higher pigment loading, such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures, such as from about 120.degree. to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, when a low gloss image of preferably from about 1 to about 30 gloss is preferred, low gloss paper is utilized, such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners of from about 3 to about 5 microns and fixing thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, if higher image gloss is desired, such as from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized such as from about 30 to about 60 gloss units, and which after image formation with small particle size toners of the present invention of from about 3 to about 5 microns and fixing thereafter results in a higher gloss toner image of from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns such that the pile height of the toner layer(s) is low.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 9 microns to about 20 microns, and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 5 microns are attained without resorting to classification processes, and where in narrow geometric size distributions are attained, such as from about 1.16 to about 1.35, and preferably from about 1.16 to about 1.30. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of this invention, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this U.S. Pat. No. '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this U.S. Pat. No. '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer such as acrylic acid in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention need not utilize a polymer with polar acid groups, and toners can be prepared with resins, such as styrene butadiene or PLIOTONE.TM., without containing polar acid groups. Additionally, the toner of the U.S. Pat. No. '127 patent does not utilize counterionic surfactant and flocculation process as does the present invention. In U.S. Pat. No. 4,983,488, a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate, which results in the formation of particles with wide GSD. Furthermore, the U.S. Pat. No. '488 patent does not disclose the process of counterionic flocculation as the present invention. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the U.S. Pat. No. '127 patent polar resins of opposite charge are selected, and wherein flocculation as in the present invention is not disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other patents mentioned are Nos. 3,674,736; 4,137,188 and 5,066,560.
In U.S. Pat. No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent and a polyester, and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising a halogenization procedure which chlorinates the outer surface of the toner and results in enhanced blocking properties. More specifically, this patent application discloses an aggregation process wherein a pigment mixture containing an ionic surfactant is added to a resin mixture containing polymer resin particles of less than 1 micron, nonionic and counterionic surfactant, and thereby causing a flocculation which is dispersed to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites or toner compositions of from about 3 to about 7 microns in volume diameter and narrow geometric size distribution of from about 1.2 to about 1.4, as measured by the Coulter Counter, and which exhibit, for example, low fixing temperature of from about 125.degree. C. to about 150.degree. C., low paper curling, and image to paper gloss matching.
In copending patent application U.S. Ser. No. 989,613 (D/92576), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant, adding thereto a counterionic surfactant with a polarity opposite to that of said ionic surfactant, homogenizing and stirring said mixture, and heating to provide for coalescence of said toner fine particles.